1. Field of the Invention
The present invention relates to a spin-valve thin-film magnetic element which undergoes a change in electric resistance in relation to the magnetization vector of a pinned magnetic layer and a magnetization vector of a free magnetic layer affected by an external magnetic field, and to a thin-film magnetic head provided with the spin-valve thin-film magnetic element. In particular, the present invention relates to a technology suitable for a spin-valve thin-film magnetic element which includes a free magnetic layer having improved soft magnetic characteristics and thus exhibits an enhanced rate of change in resistance.
2. Description of the Related Art
A spin-valve thin-film magnetic element is a type of giant magnetoresistive element (GMR) exhibiting giant magnetoresistive effects and detects recorded magnetic fields from a recording medium such as a hard disk. The spin-valve thin-film magnetic element has a relatively simple structure among GMRs, and exhibits a high rate of change in resistance in response to external magnetic fields and thus a change in resistance by a weak magnetic field.
FIG. 17 is a cross-sectional view of an exemplary conventional spin-valve thin-film magnetic element when viewed from a face opposing a recording medium (air bearing surface: ABS). This spin-valve thin-film magnetic element is a bottom-type single spin-valve thin-film magnetic element including an antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic conductive layer, and a free magnetic layer. In this spin-valve thin-film magnetic element, a recording medium such as a hard disk moves in the Z direction in the drawing, and a leakage magnetic field occurs in the Y direction in the drawing.
In the conventional spin-valve thin-film magnetic element, a composite 109 is formed on a substrate. The composite 109 includes an underlying layer 106, an antiferromagnetic layer 101, a pinned magnetic layer 102, a nonmagnetic conductive layer 103, a free magnetic layer 104, and a protective layer 107. Moreover, the spin-valve thin-film magnetic element includes, from the substrate side, a pair of hard bias layers 105 and a pair of electrode layers 108 formed on the hard bias layers, both provided on two side faces of the composite 109.
The underlying layer 106 is composed of tantalum (Ta) or the like, whereas the antiferromagnetic layer 101 is composed of a NiO alloy, an FeMn alloy, or NiMn alloy. The pinned magnetic layer 102 and the free magnetic layer 104 are composed of elemental cobalt (Co) or a NiFe alloy. The nonmagnetic conductive layer 103 is composed of a copper (Co) film. In addition, the hard bias layers 105 are composed of a cobalt-platinum (Coxe2x80x94Pt) alloy and the electrode layers 108 are composed of Cu or the like.
Since the pinned magnetic layer 102 is in contact with the antiferromagnetic layer 101, an exchange coupling magnetic field (exchange anisotropic magnetic field) is generated at the interface between the pinned magnetic layer 102 and the antiferromagnetic layer 101. The magnetization vector of the pinned magnetic layer 102 is pinned, for example, in the Y direction in the drawing.
The hard bias layers 105 are magnetized in the X1 direction in the drawing to orient the variable magnetization of the free magnetic layer 104 in the X1 direction in the drawing. As a result, the variable magnetization vector of the free magnetic layer 104 and the pinned magnetization vector of the pinned magnetic layer 102 intersect each other.
The free magnetic layer 104 includes a NiFe sublayer 104A and a Co sublayer 104B in contact with the nonmagnetic conductive layer 103.
In this spin-valve thin-film magnetic element, a sensing current is applied from electrode layers 108 to the pinned magnetic layer 102, the nonmagnetic conductive layer 103, and the free magnetic layer 104. When a leakage magnetic field is applied in the Y direction in the drawing from the magnetic recording medium moving in the Z direction in the drawing, the magnetization vector of the free magnetic layer 104 changes from the X1 direction to the Y direction in the drawing. Such a change in the magnetization vector of the free magnetic layer 104 changes electrical resistance in relation to the pinned magnetization vector of the pinned magnetic layer 102 (this change is referred to as magnetoresistive (MR) effects). As a result, the leakage magnetic field from the magnetic recording medium is detected as a change in voltage due to the change in the electrical resistance.
In such a spin-valve thin-film magnetic element, a surface oxide layer is formed at the interface between the NiFe sublayer 104A and the Co sublayer 104B in the free magnetic layer 104. This oxide layer causes an increase in resistance of the element and thus a decrease in the rate of change in resistance (xcex94R/R) in the GMR effects, resulting in deterioration of read output characteristics of the spin-valve thin-film magnetic element.
Moreover, the thickness of the Co sublayer 104B is set to be approximately 3 to 5 angstroms; hence, interdiffusion may occur between the Cu nonmagnetic conductive layer 103 and the NiFe sublayer 104A. Such interdiffusion of Cu and NiFe causes deterioration of characteristics of these layers and thus a decrease in the rate of change in resistance (xcex94R/R) in the GMR effects, resulting in deterioration of read output characteristics of the spin-valve thin-film magnetic element.
A possible means for solving the above problems is to provide a single Co layer configuration in the free magnetic layer 104. In this case, however, the coercive force Hc of the free magnetic layer 104 is undesirably large and the variation of the magnetization vector in the free magnetic layer 104 is less sensitive to the leakage magnetic field from the exterior, resulting in a reduction in detection sensitivity.
Another possible means is to provide a NiFe single free magnetic layer 104. In this case, there is no barrier layer for preventing interdiffusion of Cu and NiFe. The interdiffusion of Cu and NiFe causes significant deterioration of characteristics of these layers and thus a decrease in the rate of change in resistance (xcex94R/R) in the GMR effects, resulting in significant deterioration of read output characteristics of the spin-valve thin-film magnetic element.
FIG. 18 is a cross-sectional view of another conventional spin-valve thin-film magnetic element when viewed from a surface opposing a recording medium (ABS). This spin-valve thin-film magnetic element is a top-type single spin-valve thin-film magnetic element including an antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic conductive layer, and a free magnetic layer. In this spin-valve thin-film magnetic element, a recording medium such as a hard disk moves in the Z direction in the drawing, and a leakage magnetic field occurs in the Y direction in the drawing.
With reference to FIG. 18, an underlying layer 121 is formed on a substrate. A free magnetic layer 125 is formed on the underlying layer 121, and a nonmagnetic conductive layer 124 is formed on the free magnetic layer 125. A pinned magnetic layer 123 is formed on the nonmagnetic conductive layer 124, and an antiferromagnetic layer 122 is formed on the pinned magnetic layer 123. Moreover, a protective layer 127 is formed on the antiferromagnetic layer 122. These layers define a composite 129. A pair of hard bias layers 126 and a pair of electrode layers 128 are formed on both sides of the composite 129.
In this spin-valve thin-film magnetic element, the pinned magnetic layer 123 is magnetized in a direction which is opposite to the Y direction in the drawing.
The underlying layer 121 is composed of tantalum or the like, and the antiferromagnetic layer 122 is composed of an IrMn alloy, an FeMn alloy, or a NiMn alloy. The pinned magnetic layer 123 and the free magnetic layer 125 are composed of elemental cobalt or a NiFe alloy, and the nonmagnetic conductive layer 124 is composed of a copper film. Moreover, the hard bias layers 126 are composed of a Coxe2x80x94Pt alloy or the like and the electrode layers 128 are composed of copper or the like.
Also, in this spin-valve thin-film magnetic element, the free magnetic layer 125 includes a NiFe sublayer 125A and a Co sublayer 125B in contact with the nonmagnetic conductive layer 124. Thus, the rate of change in resistance (xcex94R/R) in the GMR effects is decreased, resulting in deterioration of read output characteristics of the spin-valve thin-film magnetic element.
FIG. 19 is a cross-sectional view of another conventional spin-valve thin-film magnetic element when viewed from a surface opposing a recording medium. This spin-valve thin-film magnetic element is a dual spin-valve thin-film magnetic element in which a nonmagnetic conductive layer, a pinned magnetic layer, and an antiferromagnetic layer are provided on one face of a free magnetic layer, and another nonmagnetic conductive layer, another pinned magnetic layer, and another antiferromagnetic layer are provided on the other face. Since two sensing layers are provided, this spin-valve thin-film magnetic element exhibits a larger rate of change in resistance compared to the above single spin-valve thin-film magnetic elements and is suitable for high-density recording.
A magnetic recording medium such as a hard disk moves in the Z direction and the direction of the leakage magnetic field from the magnetic recording medium is in the Y direction in the drawing.
The spin-valve thin-film magnetic element shown in FIG. 19 has a composite 150 including, from the bottom, an underlying layer 141, a lower antiferromagnetic layer 142, a lower pinned magnetic layer 143, a nonmagnetic conductive layer 144, a free magnetic layer 145, a nonmagnetic conductive layer 146, an upper pinned magnetic layer 147, an upper antiferromagnetic layer 148, and a protective layer 149. Hard bias layers 132 and conductive layers 133 are formed on both sides of the composite 150.
In this spin-valve thin-film magnetic element, the underlying layer 141, the lower and upper antiferromagnetic layers 142 and 148, respectively, the lower and upper pinned magnetic layers 143 and 147, respectively, the pinned magnetic layers 143 and 147, the nonmagnetic conductive layers 144 and 146, the free magnetic layer 145, the hard bias layers 132, the conductive layers 133, and the protective layer 149 are composed of the same materials as these for the underlying layers 106 and 121, the antiferromagnetic layers 101 and 122, the pinned magnetic layers 102 and 123, the nonmagnetic conductive layers 103 and 124, the free magnetic layers 104 and 125, the protective layers 107 and 127, the hard bias layers 105 and 126, and the electrode layers 108 and 128, respectively, of the single spin-valve thin-film magnetic elements shown in FIGS. 17 and 18. At least one of the underlying layer 141 and the protective layer 149 may be omitted.
Also, in this spin-valve thin-film magnetic element, the free magnetic layer 145 includes a NiFe sublayer 145A and Co sublayers 145B, which are in contact with the nonmagnetic conductive layer 144 or 146, respectively. In the dual spin-valve thin-film magnetic element having such a configuration, the above-mentioned problems will occur at the interface between the nonmagnetic conductive layer 144 and the Co sublayer 145B and the interface between the nonmagnetic conductive layer 146 and the Co sublayer 145B. Thus, the rate of change in resistance (xcex94R/R) in the GMR effects will be decreased, resulting in deterioration of read output characteristics of the spin-valve thin-film magnetic element.
The present inventors have disclosed synthetic-ferri-pinned-type single spin-valve thin-film magnetic elements, each having pinned magnetic layers separated by a nonmagnetic interlayer, in Japanese Unexamined Patent Application Publication Nos. 10-204756, 10-204763, and 10-204767. The above problems in the free magnetic layer may occur even in such a configuration.
In addition, fundamental requirements in the spin-valve thin-film magnetic elements are improving soft magnetic characteristics of the free magnetic layer, enhancing output characteristics, and improving the detecting sensitivity.
Accordingly, the present invention is provided to achieve the following objects:
(1) To improve soft magnetic characteristics of a free magnetic layer;
(2) To enhance output characteristics of a spin-valve thin-film magnetic element;
(3) To improve the detection sensitivity of the spin-valve thin-film magnetic element;
(4) To improve the rate of change in resistance (xcex94R/R); and
(5) To provide a thin-film magnetic head provided with such a spin-valve thin-film magnetic element.
A spin-valve thin-film magnetic element in accordance with the present invention comprises: a substrate; a composite provided on the substrate, the composite comprising an antiferromagnetic layer, a pinned magnetic layer in contact with the antiferromagnetic layer, the magnetization vector of the pinned magnetic layer being pinned by an exchange coupling magnetic field with the antiferromagnetic layer; a nonmagnetic conductive layer in contact with the pinned magnetic layer, and a free magnetic layer in contact with the nonmagnetic conductive layer, the magnetization vector of the free magnetic layer being oriented in a direction intersecting the magnetization vector of the pinned magnetic layer; hard bias layers provided on both sides of the composite so that the magnetization vector of the free magnetic layer intersects the magnetization vector of the pinned magnetic layer; and electrode layers provided on the hard bias layers, the electrode layers applying a sensing current to the composite, wherein the free magnetic layer comprises a single layer composed of a CoFe-based alloy.
Since the free magnetic layer in the present invention comprises a single layer comprising a CoFe-based alloy, the free magnetic layer is provided with an oxide layer. Thus, this spin-valve thin-film magnetic element does not cause an increase in resistance, a decrease in the rate of change in resistance (xcex94R/R) in the GMR effects, and deterioration of the read output characteristics of the spin-valve thin-film magnetic element, which are caused by a surface oxide layer at an interface between a NiFe sublayer and a Co sublayer which are components of a conventional free magnetic layer.
Since this configuration does not include the NiFe sublayer, the spin-valve thin-film magnetic element does not cause an increase in resistance, a decrease in the rate of change in resistance (xcex94R/R) in the GMR effects, and deterioration of the read output characteristics of the spin-valve thin-film magnetic element, which is caused by interdiffusion between the nonmagnetic conductive layer comprising copper or the like and the NiFe sublayer.
In the free magnetic layer of the present invention, it is preferable that the average diameter in the thickness direction of crystal grains constituting the free magnetic layer be substantially the same as or less than the thickness of the free magnetic layer. Moreover, the average diameter of the crystal grains constituting the free magnetic layer is preferably 150 angstroms or less and more preferably 100 angstroms or less in the plain of the free magnetic layer.
The CoFe-based alloy used in the present invention exhibits larger crystal magnetic anisotropy compared to the conventional FeNi-based alloy. When the average crystal grain diameter exceeds 150 angstroms in the free magnetic layer, the affects of magnetic anisotropy of individual crystal grains are significant in the free magnetic layer having a limited volume. When an external magnetic field to be detected is applied, the rotation of the magnetization vector in the free magnetic layer is not sensitively achieved, resulting in occurrence in magnetic hysteresis. As a result, soft magnetic characteristics, such as a coercive force Hc and anisotropic dispersion, are impaired, and the spin-valve thin-film magnetic element undergoes deterioration of read output characteristics due to low detecting sensitivity.
When average diameter of the crystal grains exceeds 100 angstroms in the plain of the free magnetic layer, the crystal magnetic anisotropy of the CoFe-based alloy is not readily moderated in the plain of the free magnetic layer, resulting in deterioration of soft magnetic characteristics of the free magnetic layer.
Preferably, the average diameter of the crystal grains constituting the free magnetic layer is 30 angstroms or more in the plain of the free magnetic layer.
When the average crystal grain diameter of the free magnetic layer is less than 30 angstroms, resistance increases due to grain boundary scattering of conduction electrons in the vicinity of individual crystal grains, although crystal magnetic anisotropy of individual crystal grains are moderated to improve soft magnetic characteristics. As a result, the spin-valve thin-film magnetic element exhibits a decreased rate (xcex94R/R) of change in resistance in the GMR effects and deterioration of read output characteristics.
Preferably, the total volume of crystal grains constituting the free magnetic layer in which the  less than 111 greater than  direction of the crystal grains is predominantly oriented substantially in a direction perpendicular to the plain of the free magnetic layer is 50 percent or less and more preferably 30 percent or less of the volume of the free magnetic layer.
When the total volume of crystal grains constituting the free magnetic layer in which the  less than 111 greater than  direction of the crystal grains is predominantly oriented substantially in a direction perpendicular to the plain of the free magnetic layer exceeds 50 percent of the volume of the free magnetic layer, the crystal magnetic anisotropy of the crystal grains in which the  less than 111 greater than  axis is predominantly oriented in the direction perpendicular to the plain of the free magnetic layer is enhanced. Thus, the magnetization vector of the free magnetic layer does not sensitively rotate even when an external magnetic field to be detected is applied, resulting in occurrence in magnetic hysteresis. As a result, soft magnetic characteristics are impaired, and the spin-valve thin-film magnetic element undergoes deterioration of read output characteristics due to low detecting sensitivity. Furthermore, the coercive force Hc of the free magnetic layer undesirably increases to decrease the detection sensitivity. Accordingly, the above-mentioned total volume of the crystal grains is preferably 50 percent or less and more preferably 30 percent or less of the volume of the free magnetic layer.
Herein, the volume of predominantly oriented crystal grains is determined by an image analysis of a cross-section of the free magnetic layer using a transmission electron microscope (TEM). Among crystal grains constituting the free magnetic layer in the TEM image, regions of the crystal grains of which the  less than 111 greater than  direction perpendicular to the (111) plane of the cubic crystal in, for example, a CoFe alloy is predominantly oriented substantially in a direction perpendicular to the plain of the free magnetic layer (hereinafter referred to as xe2x80x9cpredominantly oriented crystal grainsxe2x80x9d) are identified. This region is determined by electron diffractometry in the TEM observation. Next, the regions corresponding to the free magnetic layer is identified in the cross-sectional image. The ratio of the total area of the predominantly oriented crystal grains to the total area of the free magnetic layer is calculated. The volume ratio can be calculated by the above area ratio. The volume ratio of the grains of which the  less than 111 greater than  direction is predominantly oriented in a direction perpendicular to the plane of the free magnetic layer to the overall grains in the free magnetic layer is thereby defined.
The regions of the predominantly oriented crystal grains are identified by electron diffractometry in the TEM observation.
FIG. 12 is a transmission electron micrograph of a cross section of a dual spin-valve thin-film magnetic element, which has composites, each including a nonmagnetic conductive layer, a pinned magnetic layer, and an antiferromagnetic layer, are deposited on two surfaces of a free magnetic layer; and FIG. 13 is a schematic view for illustrating the cross-section shown in FIG. 12.
In the schematic illustration in FIG. 13 of the TEM photograph shown in FIG. 12, region S of the crystal grains of which the  less than 111 greater than  direction, which is perpendicular to the (111) plane of a cubic crystal, is predominantly oriented in the direction perpendicular to the plane of the overall free magnetic layer is identified by electron diffraction or the like. Next, regions F of the free magnetic layer are identified. The ratio by area of the regions S to the regions F is calculated to define the volume ratio of the crystal grains of which the  less than 111 greater than  direction is predominantly oriented substantially in the direction perpendicular to the plain of the free magnetic layer in the overall regions F of the free magnetic layer.
The electron diffractometry is described. A certain crystal grain constituting the free magnetic layer is irradiated with focused electron beams with a diameter of 0.5 to several nanometers to observe a transmission electron diffraction pattern of the crystal grain. The direction of the {111} diffraction spot from the center beam in the diffraction pattern is the normal direction of the {111} plane. This direction is compared to the TEM image to determine the direction of the normal direction of the {111} plane in the observed crystal grain.
When cross stripes recognized as the {111} plane in the TEM image is distinctly observed (when the distance between the cross stripes agrees with the distance of the lattice plain), the cross stripes themselves correspond to the {111} planes. Thus, the direction perpendicular to the cross stripes is identified as the  less than 111 greater than  direction, which is perpendicular to the {111} plane.
This observation is repeated for individual crystals to identify the regions of the crystal grains. In the TEM photograph shown in FIG. 12, the ratio by area of the region S to the region F is 10.3 percent.
The thickness of the free magnetic layer is in a range of preferably 10 to 50 angstroms and more preferably 15 to 30 angstroms.
When the thickness of the free magnetic layer exceeds the upper limit, the shunt loss of the sensing current occurs. When the thickness is less than the lower limit, the average free path of spin-up and spin-down conduction electrons moving in the free magnetic layer decreases. Both the cases cause a decreased rate of change in resistance (xcex94R/R) in the GMR effects, resulting in undesirable deterioration of read output characteristics of the spin-valve thin-film magnetic element.
In the present invention, the free magnetic layer may be a single CoFe layer. In this layer, cobalt may be enriched. For example, the Co/Fe ratio may be 90/10 by atomic percent.
In the cobalt-enriched composition, a rate of change in resistance (xcex94R/R) increases.
Alternatively, the free magnetic layer may be a single CoFeNi layer. Also, in this layer, cobalt may be enriched. For example, the ratio Co:Fe:Ni may be 70:15:15. In the composition near this ratio, the magnetostriction reaches zero.
At least one of the free magnetic layer and the pinned magnetic layer which are in contact with the nonmagnetic conductive layer is provided with a reflective mirror layer comprising a nonmagnetic insulating material at a face which is not in contact with the nonmagnetic conductive layer. The rate of change in resistance is thereby improved.
Examples of insulating materials for forming the reflective mirror layer include oxides, such as xcex1-Fe2O3, NiO, CoO, Coxe2x80x94Fexe2x80x94O, Coxe2x80x94Fexe2x80x94Nixe2x80x94O, Al2O3, Alxe2x80x94Qxe2x80x94O (wherein Q is at least one element selected from the group consisting of B, Si, N, Ti, V, Cr, Mn, Fe, Co, and Ni), and Rxe2x80x94O (wherein R is at least one element selected from the group consisting of Ti, V, Cr, Zn, Nb, Mo, Hf, Ta and W); and nitrides, such as Alxe2x80x94N, Alxe2x80x94Qxe2x80x94N (wherein Q is at least one element selected from the group consisting of B, Si, O, Ti, V, Cr, Mn, Fe, Co, and Ni), and Rxe2x80x94N (wherein R is at least one element selected from the group consisting of Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W).
Before describing the reasons for the increased rate of change in resistance due to the use of the reflective mirror layer, the principle of the giant magnetoresistive effects of the spin-valve thin-film magnetic element will be described with reference to an embodiment in which the reflective mirror layer is arranged at a face of the free magnetic layer which is not contact with the nonmagnetic conductive layer.
When a sensing current is applied to the spin-valve thin-film magnetic element, conduction electrons primarily move in the vicinity of the nonmagnetic conductive layer having small electrical resistance. There are two types of conduction electrons, that is, spin-up conduction electrons and spin-down conduction electrons are present in the same quantity. The rate of change in resistance of the spin-valve thin-film magnetic element has a positive correlation with the difference in mean free path of conduction electrons between these two types.
The spin-down conduction electrons are always scattered at the interface between the nonmagnetic conductive layer and the free magnetic layer regardless of the vector of the applied external magnetic field, and has a low probability of moving to the free magnetic layer and a mean free path which is always smaller than that of spin-up conduction electrons.
In contrast, the spin-up conduction electrons has a higher probability of moving from the nonmagnetic conductive layer to the free magnetic layer and a larger mean free path when the magnetization vector of the free magnetic layer is parallel to the magnetization vector of the pinned magnetic layer by an external magnetic field. When the external magnetic field changes the magnetization vector of the free magnetic layer rotates from the parallel arrangement, the probability of electron scattering at the interface between the nonmagnetic conductive layer and the free magnetic layer increases and thus the mean free path of the conduction electrons decreases.
As described above, the mean free path of spin-up conduction electrons considerably changes compared with the mean free path of spin-down conduction electrons due to the effects of the external magnetic field, and thus the difference in the mean free path is considerably increased. Accordingly, the rate of change in resistance (xcex94R/R) of the spin-valve thin-film magnetic element increases due to a change in resistivity.
When the reflective mirror layer is deposited at a face not in contact with the nonmagnetic conductive layer of the free magnetic layer, the mirror reflective layer forms a potential barrier at the interface with the free magnetic layer so as to reflect the spin-up conduction electrons on the mirror surface while maintaining the spin state. As a result, the mean free path of the spin-up conduction electrons can be further increased. That is, the difference in mean free path between the spin-dependent conduction electrons is further increased by the specular effects, the rate of change in resistance of the spin-valve thin-film magnetic element is further improved.
When the mirror reflective layer is deposited on a face not contact with the nonmagnetic conductive layer of the pinned magnetic layer, the mirror reflective layer also forms a potential barrier at the interface with the pinned magnetic layer so as to reflect the spin-up conduction electrons on the mirror surface while maintaining the spin state. As a result, the mean free path of the spin-up conduction electrons can be further increased. That is, the difference in mean free path between the spin-dependent conduction electrons is further increased by the specular effects, the rate of change in resistance of the spin-valve thin-film magnetic element is further improved.
In the composite of the spin-valve thin-film magnetic element of the present invention, the antiferromagnetic layer, the pinned magnetic layer, the nonmagnetic conductive layer, and the free magnetic layer may be deposited in that order on the substrate (bottom type).
Alternatively, in the composite, the free magnetic layer, the nonmagnetic conductive layer, the pinned magnetic layer, and the antiferromagnetic layer may be deposited in that order on the substrate (top type).
Alternatively, in the composite, the nonmagnetic conductive layer, the pinned magnetic layer, and the antiferromagnetic layer may be deposited on one face in the thickness direction of the free magnetic layer, and the composite further may comprise another nonmagnetic conductive layer, another pinned magnetic layer, and another antiferromagnetic layer being deposited on the other face of the free magnetic layer (dual type).
The bottom type can directly supply a larger proportion of sensing current from the electrode layers to the composite without via the antiferromagnetic layer having high resistivity compared to the top type. Moreover, the bottom type reduces shunt components of the detecting current which directly flow in the pinned magnetic layer, the nonmagnetic conductive layer, and the free magnetic layer from the hard bias layers, unlike the top type. Since side reading is prevented, the bottom type is advantageous for higher recording densities.
In the dual type, the number of the interfaces between the free magnetic layer and the nonmagnetic conductive layers is two times that of the bottom or top type. Since these interfaces function as filters for spin-up conduction electrons, a larger rate of change in resistance is achieved compared to the above single spin-valve thin-film magnetic elements, resulting in higher output.
In the spin-valve thin-film magnetic element of the present invention, the pinned magnetic layer may comprise a nonmagnetic interlayer and first and second pinned magnetic sublayers sandwiching the nonmagnetic interlayer, the magnetization vectors of the first and second pinned magnetic sublayers being antiparallel to each other and the first and second pinned magnetic sublayers being in a ferri-magnetic state. That is, this spin-valve thin-film magnetic element is of a so-called synthetic ferri-pinned type. In the pinned magnetic layer of the synthetic ferri-pinned type, the magnetostatic coupling magnetic field of the first pinned magnetic sublayer and the magnetostatic coupling magnetic field of the second pinned magnetic sublayer is mutually offset. Thus, this configuration suppresses the demagnetizing field (dipole magnetic field) due to the pinned magnetization of the pinned magnetic layer. As a result, the variable magnetization vector of the free magnetic layer is less affected by the demagnetizing field (dipole magnetic field) in the synthetic ferri-pinned type.
Moreover, one of the first and second pinned magnetic sublayers separated by the nonmagnetic conductive layer can pin the other in an appropriate direction. Thus, the pinned magnetic layer exhibits a considerably stable sate.
The pinned magnetic layer having the above double layer configuration (synthetic-ferri-pinned-type pinned magnetic layer) reduces the affect of the demagnetizing field (dipole magnetic field) by the pinned magnetization of the pinned magnetic layer on the free magnetic layer, the variable magnetization vector of the free magnetic layer can be corrected to a desired direction. As a result, the spin-valve thin-film magnetic element exhibits slight asymmetry and the variable magnetization vector of the free magnetic layer can be more readily controlled.
Herein the term xe2x80x9casymmetryxe2x80x9d indicates the degree of the asymmetry of the read output waveform. When the read output waveform is symmetry, the asymmetry becomes zero. When the variable magnetization vector of the free magnetic layer is orthogonal to the pinned magnetization vector of the pinned magnetic layer, the asymmetry is zero. If the asymmetry is much larger than zero, the spin-valve thin-film magnetic element cannot exactly read information on a medium. As the asymmetry approaches zero, the spin-valve thin-film magnetic element can process read output with high reliability.
The demagnetizing field (dipole magnetic field) Hd due to the pinned magnetization of the pinned magnetic layer has an uneven distribution in which the field is large in the peripheries and is small in the center in the height direction. The single-domain alignment in the free magnetic layer may be inhibited in conventional configurations. In the present invention, the dipole magnetic field Hdsubstantially is zero due to the multilayered pinned magnetic layer. Since the free magnetic layer is aligned in a single-domain state, the spin-valve thin-film magnetic element does not generate Barkhausen noise and can exactly process signals from a magnetic recording medium.
In the spin-valve thin-film magnetic element, the antiferromagnetic layer preferably comprises one of an Xxe2x80x94Mn alloy and a Ptxe2x80x94Mnxe2x80x94Xxe2x80x2 alloy wherein X is one element selected from the group consisting of Pt, Pd, Ir, Rh, Ru, and Os, and Xxe2x80x2 is at least one element selected from the group consisting of Pd, Cr, Ru, Ni, Ir, Rh, Os, Au, Ag, Ne, Ar, Xe, and Kr. Preferably, the X content is in a range of 37 to 63 atomic percent and the total content of Xxe2x80x2 and Pt is in a range of 37 to 63 atomic percent.
The Xxe2x80x94Mn alloys and the Ptxe2x80x94Mnxe2x80x94X alloys exhibit higher exchange coupling magnetic fields and blocking temperatures and higher corrosion resistance compared to NiO alloys, FeMn alloys, and NiMn alloys, which are conventionally used in antiferromagnetic layers.
In this spin-valve thin-film magnetic element, Cr bias underlayers may be provided between the hard bias layers and the composite and between the hard bias layers and the substrate. Since chromium of the bias underlayers has a body-centered cubic crystal structure, the hard bias layers can have a large coercive force and a high remanence ratio. As a result, the bias magnetic field can be further increased to completely align the free magnetic layer into the single-domain state.
A thin-film magnetic head in accordance with the present invention comprises the above-mentioned spin-valve thin-film magnetic element.